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Sliding Hockey Puck

  • Thread starter kchurchi
  • Start date
  • #1
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Homework Statement


A hockey puck is sliding across a frozen pond with an initial speed of 7.5 m/s. It comes to rest after sliding a distance of 23.7 m. What is the coefficient of kinetic friction between the puck and the ice?

v0x = initial speed = 7.5 m/s
vfx = final speed = 0 m/s
Δx = x distance traveled = 23.7 m
fk,IP = force of kinetic friction from ice on puck
NIP = normal force from ice on puck
WEP = weight force from earth on puck
mP = mass of puck
g = acceleration due to gravity

Homework Equations


ƩFnet = m*a
ƩFx = -fk,IP = m*ax
ƩFy = NIP - WEP = m*ay → ay = 0 m/s^2 → NIP = mP*g

The Attempt at a Solution


I attempted this logic...

fk,IP = μk*NIP → (-m*ax)/(mP*g) = μk

But then I hit a wall when trying to find the x-acceleration. Help?
 

Answers and Replies

  • #2
6,054
390
You need the equation of distance traveled under constant acceleration (deceleration in this case).
 
  • #3
39
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I am not allowed to have the equations of constant acceleration to solve problems. I must derive all equations myself using calculus. How do I even know that the acceleration is constant?
 
  • #4
537
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there's only one force acting on the puck in the x-direction: the frictional force

and it depends on two constant values: the coefficient of friction and the normal force on the puck

therefore, the force is constant, therefore the acceleration is constant

set up the equation of motion

[itex]\Sigma F = m\ddot{x} = F_{friction}[/itex]

and go from there

I'm assuming that since they want you to derive the equations yourself, that you know how to do a differential equation, right?
 

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